Process for regulating a refrigerating system, refrigerating system and expansion valve

ABSTRACT

In a process for regulating a refrigeration system (1) using an expansion valve (4), one side of the regulating member is pressed by the pressure of refrigerant at the evaporator side and the other side of the regulating member is pressed by the vapor pressure of a sensor system (22) whose sensor temperature is determined by the refrigerant saturation temperature and by the heat supplied by a heating element (27). heat supply is regulated depending on a measurement value (overheating or liquid level). Also disclosed is a refrigeration system (1) regulated in this manner and an expansion valve (4) as essential component of such a system. An improved, exonomic and universally applicable regulation can thus be obtained.

The invention relates to a method for controlling a refrigerationsystem, to a refrigeration system and to an expansion valve for such arefrigeration system.

From WO 82/04142 is known a refrigeration system having in series acompressor, a condenser, an expansion valve and an evaporator. Thissystem is controlled by the expansion valve having as actuator adiaphragm or a bellows and can be acted upon by a heat supply from aheating element. One side of the actuator is biased by the vapourpressure of a liquid-vapour filled sensor system, whose sensortemperature is determined by heat supply. The superheat is measured onthe outlet side of the evaporator, and the heat supply is controlled independence of the measured value. The heatable sensor is mounted on theoutlet side refrigerant line of the evaporator, where superheatedrefrigerant vapour is already available. Therefore, the heat dissipationis relatively low and changes concurrently with the superheattemperature.

From DE 40 05 728 A1 is known a refrigeration system, which iscontrolled in dependence on superheat at the evaporator outlet. For thatpurpose, the expansion valve has an actuator in the form of a diaphragm,one side of which is biased by the refrigerant pressure at theevaporator outlet and the other side of which is biased by a pressurecorresponding to the refrigerant temperature at the evaporator outlet.This control requires either the intake line leading to the compressoror a measuring line in the form, for example, of a capillary tube, to berun right up to the expansion valve. This frequently leads torestrictions in the design of the refrigeration system. In addition, thecontrol is often very unstable, with wildly fluctuating superheat.

In the known case, this superheat control has an additional influenceimposed on it, derived from the temperature in the line betweencompressor and condenser. For that purpose, one of the two pressurechambers of the diaphragm capsule is filled with a control medium, whichthrough the diaphragm capsule is heated by heat-exchange with thesuperheated refrigerant at the outlet of the evaporator and isadditionally heated by a heating element, for example, a PTC resistor.

From U.S. Pat. No. 3,313,121 is known a refrigeration system and amethod for controlling a refrigeration system by means of an expansionvalve having as actuator a diaphragm, one side of the diaphragm beingacted upon by the refrigerant pressure on the outlet side of theexpansion valve, the other side being acted upon by the pressure of asensor mounted on the superheat path of the evaporator.

The invention is based on the problem of improving control of arefrigeration system using simple and inexpensive means.

In this practical form the sensor is in continuous thermal contact withliquid refrigerant, which gives a good heat transmission atsubstantially constant temperature conditions. The opening degree of thevalve is determined substantially by the heat supply by means of theheating element, since it is by the heating that the vapour pressure inthe sensor system is increased, as the heating increases the pressure inthe sensor system. The filling, whose pressure is temperature dependent,can either be a liquid-vapour filling or an adsorption filling. Here,the vapour pressure is a function of the temperature and increases withincreasing temperature. The greater is the power supplied to the heatingelement, the greater is the opening degree of the valve. Proportionalityis practically achieved by the following relationship:

    E-K×A×(T.sub.f -T.sub.s)

E=the power supplied to the heating element

K=heat transfer coefficient

A=heat transfer surface between sensor and refrigerant

T_(f) =sensor temperature

T_(s) =saturation temperature of the refrigerant at the valve outlet.

This relationship applies regardless of how high saturation pressure andsaturation temperature of the refrigerant at the valve outlet are at thetime. The opening degree of the valve is therefore independent of theevaporator pressure. Any compensation by means of the heating element isnot necessary.

Since the heat supply is controlled, that is, is pre-set by acontroller, all automatic control engineering options can be applied toimprove the control, for example a PI controller can be used. Moreover,further miscellaneous functions, such as a dependency on compressorspeed, icing up, or undue increase in temperature of the compressedrefrigerant, can be taken into account. This enables control to be veryaccurate. A further advantage consists in that the expansion valvecloses when the heating element fails.

The refrigerant pressure or the refrigerant temperature only need to bedetected at the outlet side of the expansion valve. A line connectionbetween the outlet of the evaporator and the expansion valve is notrequired. Simple signal lines suffice for the connection between themeasuring points and the controller, and a simple electrical leadprovides the connection between the controller and the heating element.This results in a simple and inexpensive construction. When adapting therefrigeration system to a specific application the line layout can bechosen with greater freedom than previously. The control principle issuitable not only for dry evaporators, in which superheat is measured,but also for flooded evaporators, in which the level of liquid is usedas measuring value. All this allows very versatile use.

In another form of the invention a small amount of refrigerant iscontinuously released, also when the expansion valve is closed.

In accordance with the apparatus according to the invention, providingare two alternatives for the detection of the saturation temperature.

When, the tube is a capillary tube, this tube can form both the bypasschannel and the second throttling point. This double function savesadditional components.

It is recommendable when, the outlet channel is connected with theoutlet side of the expansion valve. The expression "outlet side of theexpansion valve" includes the entire region between the throttle pointof the expansion valve and the actual inlet of the evaporator, even whenchangeover valves, distributors or other built-in components arepresent. There is therefore considerable freedom of scope for mountingthe sensor and the compensating channel.

It is especially advantageous, however, for these components to bearranged close to the expansion valve, because then the connectingroutes involved are short. However, it is also important that thepressure in the compensating channel is equal to the pressure in themounting spot of the temperature sensor.

When the compensating channel is from a refrigerant line at the outletof the expansion valve to one of the pressure chambers, only a shortpipe is needed to connect the refrigerant line to the one pressurechamber.

An even cheaper solution is provided if the compensating channel isrouted in the interior of the valve.

The capillary tube connected from the sensor to the pressure chamberresults in a clear separation of the sensor temperature and thetemperature in the pressure chamber.

In the construction the refrigerant line adjoining the outlet of theexpansion valve forms a preferred carrier for sensor and heatingelement. A strap retainer can be used for fastening.

In one form of the invention, the sensor is arranged in or on the outletside housing part of the expansion valve, wherein in another form of theinvention the sensor can be formed by a chamber in the housing part.

In a preferred embodiment of the invention, the heating element isarranged inside the sensor. This produces an even better heat transferand facilitates assembly.

The heat insulation covering the sensor or the heating element helpsprevent faults through heat radiation into the surroundings.

An important component of the refrigeration system, which is alsotreated separately, is the expansion valve. All necessary elements arelocated in the expansion valve or in the immediate vicinity thereof.

For practical operation, it is advantageous when, the valve housing, thecompensating channel and the sensor system form a pre-assembled module,which may include, the refrigerant line adjoining the valve outlet.

Advantageously, the expansion valve can also be provided with a bypasschannel.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in greater detail hereinafter with referenceto preferred embodiments illustrated in the drawings, in which:

FIG. 1 is a circuit diagram of a refrigeration system according to theinvention with a through-flow evaporator,

FIG. 2 is a diagrammatic view of an expansion valve,

FIG. 3 is a section along the line A--A in FIG. 2,

FIG. 4 is a diagrammatic view of a modified expansion valve,

FIG. 5 is a circuit diagram of a modified refrigeration system accordingto the invention with a flooded evaporator,

FIG. 6 shows a modified sensor,

FIG. 7 is a diagrammatic view of a further alternative of a modifiedexpansion valve,

FIG. 8 a section of a further embodiment of a refrigeration systemaccording to the invention,

FIG. 9 a further embodiment of an expansion valve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a refrigeration system 1 in which a compressor 2 for therefrigerant, a condenser 3, an expansion valve 4 and a dry evaporator 5are arranged one behind the other in series. A dry evaporator shall beunderstood to mean an evaporator in which all the refrigerant isevaporated during a single passage through the evaporator.

The expansion valve 4 can be of the form, for example, illustrated inFIG. 2. A valve housing 6 has an inlet chamber 7 and an outlet chamber8, between which a valve seat 9 is located. The associated closuremember 10 is carried by a valve stem 11, which co-operates with anactuator 12 in a diaphragm box 13. The closure member 10 is acted uponby a spring 14, the mounting plate 15 of which spring is adjustable bymeans of an adjusting device 16; the closure member is also acted uponby the pressure pK in a lower pressure chamber 17 and in the oppositedirection is acted upon by the pressure pT in an upper pressure chamber18. A refrigerant line 19 in the form of a copper pipe is connected tothe chamber 8 located on the outlet side. The refrigerant line'sinterior is connected by way of a compensating channel 20 in the form ofa pipe to a connector 21, which leads to the lower pressure chamber 17.The pressure pK therefore corresponds to the refrigerant pressure at theoutlet of the expansion valve 4.

The upper pressure chamber 18 is part of a sensor system 22, the sensor23 of which is connected by way of a capillary tube 24 to the upperpressure chamber 18. The sensor 23 is located with a first wall portion25 against the refrigerant line 19. A second wall portion 26 on theopposite side serves for mounting an electrically heatable heatingelement 27. A retaining means 28, for example a strap or band, serves tosecure the sensor 23 and the heating element 27 to the refrigerant line19. Current supply to the heating element 27 is effected by way of anelectrical lead 29. The sensor system 22 contains a liquid-vapourfilling, which means that the pressure pT in the pressure chamber 18 isthe same as the saturation pressure of the filling medium at theparticular sensor temperature.

As furthermore shown in FIG. 1, for operation of the expansion valve 4only a single connecting element, namely, the electrical lead 29, has tobe taken into the region of the expansion valve 4. The heat output to bedelivered by the heating element 27 is pre-set by a controller 30, whichreceives as actual value the instantaneous superheat, that is thedifference between the actual refrigerant temperature and the saturationtemperature. For that purpose, in known manner, the refrigeranttemperature is measured with a temperature sensor 31, which is locatedon the outlet line 32 of the evaporator, and the refrigerant pressure,which is equivalent to the saturation temperature, is measured with apressure sensor 33, which is connected to the interior of the line 32.The measured values are supplied to the controller 30 via signal lines34 and 35. The sensors 31 and 33 can be electronic sensors that transmitelectrical signals via the signal lines. An inlet 36 indicates that yetfurther influences apart from superheat can be made operative.

The filling medium in the sensor system is chosen with reference to therefrigerant so that with no heating the sensor pressure pT above theactuator is somewhat higher than the refrigerant pressure pK below theactuator. The pressure ratios are matched, however, so that by virtue ofthe spring 14 the force acting from below is somewhat larger than theforce acting from above. The expansion valve is therefore closed whenthere is no heating. Just a slight supply of heat is sufficient,however, to open the valve. In addition, precautions are taken to ensurethat the summation curve of spring force and refrigerant pressure pK inthe control range is an approximately constant distance from the curveof the sensor pressure pT. By means of the spring 14 a value ofsuperheat, for example, 4°, is set. As soon as this is exceeded, theexpansion valve opens.

In operation, a reference value is set at the controller 30, preferablya PI controller, and is compared with the measured value of superheat.In dependence on the deviation of the measured values from the referencevalue, the heat output is controlled so that continuous operation withfew fluctuations is achieved. In this connection the opening degree ofthe valve is proportional to the heat output supplied, irrespective ofthe level of the evaporator pressure in the refrigerant line 19.

It is furthermore apparent from FIG. 2 that although the expansion valveitself is a standard valve, supply to the connections of the twopressure chambers 17 and 18 is effected in a novel manner. Because allconnections can be made just after the expansion valve, valve housing 6,compensating channel 20, sensor system 22 and refrigerant line 19 can bedelivered in the form of a pre-assembled module.

The electrical lead 29 and the signal lines 34 and 35 can be installedwithout difficulty in the appliance containing the refrigeration system,which contributes to a further reduction in costs.

In FIG. 4, reference numbers increased by 100 have been used forcorresponding parts. One difference is that the compensating channel 120is provided in the form of an internal bore in the housing 106. Inaddition, a chamber in the valve housing 106 serves as sensor 123, thechamber with one wall portion 125 adjoining the chamber 108 of the valvehousing 106 located on the outlet side, and on the other side having awall portion 126 which, unencumbered, faces outwards and serves formounting the heating element 127. Sensor 123 and heating element 127 arecovered by heat-insulation 137 to prevent loss by radiation to theoutside.

In this construction a new kind of valve is provided, which has all theessential features in and on its housing, and which can be pre-assembledas a module, with or without the refrigerant line 119.

With the refrigeration system 201 in FIG. 5, for identical parts thesame reference numbers as in FIG. 1 are used, and for modified partsreference numbers increased by 200 are used. Here, a flooded evaporator205 is used, which is connected by an upper line 238 and a lower line239 to a collector 240. In the form of a mixture of liquid and vapour,the refrigerant flows back via the upper line 238 into the collector240, whilst liquid refrigerant flows via the lower line 239 to theevaporator 205. This circulation takes place automatically, but can alsobe assisted by a pump. A fill level indicator 231 informs the controller30 of the liquid level and the controller sets the opening degree of theexpansion valve 4 so that a desired fill level is maintained.

In the case of the sensor 323 illustrated in FIG. 6, the heating element327 is arranged inside the sensor. Such a sensor can be secured to therefrigerant line 19 using a retaining means similar to the retainingdevice 28.

Refrigeration systems having several evaporators connected in parallelcan also, of course, be operated in the described manner. In that casethe sensor can be arranged either before the distributor or in one ofthe branch lines after the distributor. Superheat can also be measuredin a manner other than as illustrated in FIG. 1, for example by atemperature sensor before and a temperature sensor after the evaporator.The pipe-form compensating channel of FIG. 1 can also be combined withthe sensor associated with the housing according to FIG. 5, orconversely the internal compensating channel according to FIG. 5 can becombined with the sensor according to FIG. 1 or 6 located on therefrigerant line.

FIG. 7 shows a diagrammatic view of an expansion valve 404, whoselocking piece, together with the valve seat, forms a first throttlingpoint 441. A bypass channel 442 bridges this throttling point 441. Itleads from the inlet connector 443 of the valve housing 406 to theoutlet connector 444, and comprises in series a line section 445 withsmall cross section, a fixed second throttling point 446 in the shape ofa small opening, and an expansion chamber 447. A sensor 423 is mountedon the wall of the expansion chamber 447, which sensor is in thermalcontact with a heating element 427 on the opposite side, and isconnected with the upper pressure chamber 418 via a capillary tube 424.The pressure chamber 417 is acted upon by the outlet side pressure ofthe refrigerant.

With this construction the refrigerant in the expansion chamber 447assumes the saturation temperature, which is also the temperature of therefrigerant at the outlet of the expansion valve 404.

In the embodiment according to FIG. 8, reference numbers increased by100 are used for corresponding parts in FIG. 7. As opposed to FIG. 7,the bypass channel 542 does not only bridge the first throttling point541 of the expansion valve 504, but also the complete evaporator 5, thatis, it leads from the inlet connector 543 of the expansion valve 504 tothe outlet line of the evaporator 5. Again, the sensor 523 is mounted onthe wall of the expansion chamber 547 and is heated by a heating element527. To take into consideration the pressure drop in the evaporator 5,the pressure chamber 517 is connected with the outlet line 532 via acompensating channel 520 in the shape of a capillary tube.

FIG. 9 shows an additional modified form of an expansion valve, in whichreference numbers of corresponding parts are increased by 600 inrelation to FIGS. 1 to 3.

Initially, it can be seen that the valve 604 in FIG. 9 has been turnedin relation to the previously shown embodiments. In this embodiment ofthe invention, the compensating channel 620 is arranged inside the valve604, like in FIG. 4. Otherwise, the valve 604 is substantially equal tothat shown in FIG. 2.

In the embodiment in FIG. 9 a separate sensor is not provided. Instead,the heating element 627 is arranged direct on the housing 606 of thevalve 604 on the sensor chamber 618. An electrical cable 629 leads tothe controller 30, as described above.

In this embodiment of the invention, the heat is led direct to thesensor chamber 618 through the heating element 627, without requiring aseparate sensor or capillary tube. This makes the valve 604 simpler thanthe embodiments of the invention shown above. To provide a correct andeffective heating of the medium in the sensor chamber 418, however, thevalve 604 must be turned.

The mode of operation according to the invention will now be describedin detail. In each form of the invention, be it with separate sensors23, 123, 323, 423 or 523, or the embodiment in which the heating element627 supplies the heat direct to the expansion valve 604, the valveopens, when the pressure in the sensor chamber 18 exceeds the sum of thepressure in the pressure chamber 18 and the power of the spring 14. Inthe embodiment of the invention using a sensor, most of the energyprovided by the heating element 27, 127 or 327 will flow into the mediuminside the sensor, even though a small share will flow through the wallof the sensor past the medium. Heat from the heating element causes theliquid medium to boil, and vaporised refrigerant throws bubbles upwardsto the upper part of the sensor, where the temperature is lower. Therefrigerant vapour condenses under dissipation of heat to the upper sideof the sensor, which is mounted on the outlet of the expansion valve. Atthe same time, the pressure inside the sensor increases, this pressurebeing applied on the sensor chamber 18, and the valve opens.

In a similar way, in the embodiment according to FIG. 9, heat producedby the heating element 627, is brought direct into the medium, which isarranged inside the sensor chamber 618. Heat from the heating elementcauses the liquid medium in the sensor chamber 618 to boil, whichincreases the pressure inside the sensor chamber 618 and thus opens thevalve 604. At the same time refrigerant bubbles rise upwards in thesensor chamber 618 to areas in which the temperature is lower. Here thevapour condenses under dissipation of heat to the surrounding liquid,and the heat is then led through the actuator 612 into the pressurechamber 617. Thus, there is a constant transfer of heat to therefrigerant flowing through the valve 604, in the same way as in thefirst embodiment of the invention, in which there is a constant heattransfer from the sensor 23, 123 or 323 to the outlet pipe 19 comingfrom the evaporator valve.

What is claimed is:
 1. In a refrigeration system comprising in series acompressor, a condenser, an expansion valve and an evaporator, a methodof controlling the refrigeration system by means of the expansion valve,the expansion valve comprising an actuator having one of a diaphragm anda bellows and being arranged to be acted upon by heat supplied by aheating element, comprising the steps of biasing one side of theactuator by refrigerant pressure from the evaporator, biasing the otherside of the actuator vapour pressure of a sensor system whose pressureis temperature dependent, determining the temperature of the sensorsystem by the saturation temperature of the refrigerant and by the heatsupplied by the heating element, and measuring one of superheat on theoutlet side of a dry evaporator and the liquid level of a floodedevaporator and regulating heat supplied by the heating element independence on the measured superheat.
 2. Method according to claim 1, inwhich one side of the actuator is acted upon by the refrigerant on theoutlet side of the expansion valve.
 3. Method according to claim 1, inwhich the sensor temperature at the outlet side of the expansion valveis influenced by the saturation temperature of the refrigerant. 4.Method according to claim 1, in which part of the refrigerant is ledpast a throttling point of the expansion valve and including a fixedsecond throttling point, the sensor being located after the secondthrottling point and being influenced by the saturation temperature ofthe refrigerant.
 5. Refrigeration system comprising in series acompressor, a condenser, an expansion valve having an inlet and anoutlet, and an evaporator, the expansion valve comprising an actuatordivided into two pressure chambers, one of a diaphragm and a bellowsdividing the chambers and being arranged to be acted upon by heatprovided by means of a heating element, a compensating channelconnecting one of the pressure chambers with a refrigerant path leadingto the evaporator, the other pressure chamber comprising part of asensor system having a sensor fluid whose pressure is temperaturedependent, the sensor system having a sensor in thermal contact withrefrigerant at the outlet of the expansion valve and with the heatingelement, and a controller connected to control the heating element independence on one of superheat at an outlet of the evaporator and on theliquid level of a flooded evaporator.
 6. Refrigeration system,comprising in series a compressor, a condenser, an expansion valvehaving an inlet and an outlet, an evaporator and a bypass channelbridging a throttling point of the expansion valve and a fixed secondthrottling point at a subsequent expansion chamber, the expansion valvecomprising an actuator having one of a diaphragm and a bellows dividingtwo pressure chambers and being acted upon by heat supplied by a heatingelement, one pressure chamber being connected to an evaporator siderefrigerant path via a compensating channel, the other pressure chamberbeing part of a sensor system having a sensor fluid, whose pressure istemperature dependent, the sensor system having a sensor inheat-exchange with refrigerant in the expansion chamber and with theheating element, and a controller connected to control the heatingelement in dependence on one of superheat at an outlet of the evaporatorand the liquid level of a flooded evaporator.
 7. Refrigeration systemaccording to claim 6, in which the bypass channel is a capillary tube.8. Refrigeration system according to claim 6, in which the compensatingchannel is connected to the outlet of the expansion valve. 9.Refrigeration system according to claim 6, in which at least one of thecompensating channel and the sensor is closely adjacent to the expansionvalve.
 10. Refrigeration system according to claim 5, in which thecompensating channel comprises a pipe that connects a refrigerant lineadjoining the outlet of the expansion valve to a connector leading toone of the pressure chambers.
 11. Refrigeration system according toclaim 5, in which the compensating channel is located inside the valve.12. Refrigeration system according to claim 5, in which the sensor isconnected by a capillary tube to the other pressure chamber. 13.Refrigeration system according to claim 5, in which the sensor issituated on the refrigerant line adjoining the outlet of the expansionvalve and is contacted by the heating element.
 14. Refrigeration systemaccording to claim 13, in which the sensor and the heating element aresecured to the refrigerant line by a retaining device.
 15. Refrigerationsystem according to claim 5, in which the sensor is arranged at ahousing part of the expansion valve located on the outlet side and iscontacted by the heating element.
 16. Refrigeration system according toclaim 15, in which the sensor comprises a chamber in the housing partlocated on the outlet side.
 17. Refrigeration system according to claim7, in which the sensor is mounted on a wall of the expansion chamber.18. Refrigeration system according to claim 7, in which the bypasschannel bridges the evaporator and that the compensating channel isconnected with the refrigerant line downstream of the evaporator. 19.Refrigeration system according to claim 7, in which on the outlet sideof the expansion valve the bypass channel flows into the refrigerantline.
 20. Refrigeration system according to claim 5, in which theheating element is arranged inside the sensor.
 21. Refrigeration systemaccording to claim 5, in which at least one of the sensor and theheating element is covered by a heat insulation.
 22. Expansion valve fora refrigeration system, having a valve housing having an inlet and anoutlet, and a valve seat located between an inlet chamber and an outletchamber, an actuator located between two pressure chambers, the actuatorcomprising one of a diaphragm and a bellows for the operation of aclosure member, and including a heating element, a compensating channelconnecting the outlet chamber and one of the pressure chambers and theother pressure chamber comprising part of a sensor system filled with asensor fluid, the sensor system having a sensor located forheat-exchange with outlet refrigerant from the expansion valve and withthe heating element.
 23. Expansion valve according to claim 22, in whichthe valve housing, the compensating channel and the sensor system form apre-assembled module.
 24. Expansion valve according to claim 22, inwhich the sensor is connected by a capillary tube to the other pressurechamber.
 25. Expansion valve according to claim 22, in which the sensoris located proximate the valve housing.
 26. Expansion valve according toclaim 23, in which a refrigerant line adjoining the valve outlet is partof the module and serves as carrier for the sensor and the heatingelement.
 27. Expansion valve according to claim 22, in which the heatingelement is located externally on the sensor.
 28. Expansion valveaccording to claim 22, in which the heating element is located insidethe sensor.
 29. Expansion valve according to claim 22, in which thecompensating channel comprises a pipe which connects the outletrefrigerant with the one pressure chamber.
 30. Expansion valve accordingto claim 22, in which the compensating channel is located inside thevalve housing.
 31. Expansion valve according to claim 22, in which theinlet and the outlet of the expansion valve are connected by a bypasschannel having a fixed throttling point with an adjacent expansionchamber, and the sensor is mounted on a wall of expansion chamber.